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Tropical Storm Alvin Winds: 55 kt
Pressure: 995 mbar
Advisory 9 / June 27, 2019

Tropical Storm Alvin Discussion Number 9

Wiki-Hurricanes Forecast Center

2:00 PM PDT Thu Jun 27 2019

Despite looking rather unimpressive on infrared imagery - and visible imagery in the morning - changes are afoot, and Alvin appears to be finally meshing its looks with its intensity. Within the last hour, an eye has begun to emerge on visible satellite imagery. This is aligned well with a 1916z GMI microwave pass which showed a fully enclosed eye about 16 nmi in diameter. Alvin's intensity is somewhat hard to diagnose, complicated by its small size. ASCAT passes at 1642z and 1708z both indicated a small region > 45 kt of winds in the northwestern quadrant, with the former pass showing one 50 kt region. SAB remained at T3.0/45kt while CIMSS-ADT is now T3.6/57kt. Microwave estimates have gone bonkers with their pressure estimates and are likely overreacting to the emergence of the eye and resultant warm core aloft. Given the improvements, a good fix from ADT and good scans from ASCAT, the intensity for this advisory has been increased to 55 kt. Despite the eye, we'll need to see good concordance between scatterometer and infrared structure - which remains rather disheleved - before estimating much higher.

Alvin has been tracking towards the west-northwest throughout the afternoon. Models are largely in consensus regarding this continued track as Alvin steers around ther periphery of an extensive ridge aloft centered over the Gulf of Mexico before the storm weakens and drifts west with the tradewinds. Alvin has about 12 or so hours over favorable waters before it reaches a sharp thermocline where temperatures fall about 1 degree every 30 miles. Coincident with this is an increase in wind shear, soon to be north of 20 kt, as it engages with a TUTT. Additional intensification is possible in the interim as Alvin fully divorces from the monsoon trough's vorticity and reaches a divergence max, and current trends are indicative of this possibiliy. The stable cool waters of the Pacific should induce weakening thereafter, and rather quickly given the storm's small size.


FORECAST MAX WINDS

INIT 27/2100Z 55 KT 65 MPH

12H 28/0600Z 60 KT 70 MPH

24H 28/1800Z 45 KT 45 MPH

36H 29/0600Z 30 KT 35 MPH

48H 29/1800Z 20 KT 35 MPH...POST-TROP/REMNT LOW

72H 30/1800Z...DISSIPATED

Forecaster TheAustinMan
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